This proposal describes a laboratory-controlled study of prestimulation modulation of startle in school-age children with PTSD. Since the specific type of startle modulation being studied in this experiment in humans is comparable to that which has been well elucidated in animals, the results can be interpreted in terms of the underlying functional neuroanatomy. Three groups of subjects will be studied. The first group will include children who meet diagnostic criteria for PTSD between 3-5 months after being exposed to a circumscribed life-threatening violent event, where the child was either the intended victim or a proximal witness to violent life-threat to a family member or friend. The second group will include children who were similarly exposed, but do not meet diagnostic criteria for PTSD between 3-5 months after exposure. The third group will consist of matched normal control subjects from the same communities. The prestimulation modulation of startle experiment will test for dysfunction of a brain stem modulating mechanism. This study will increase the understanding of a possible core neurophysiologic alteration underlying an important symptom of increased arousal in children with PTSD. The age range of the subjects will be 8 to 12 years. This age interval represents a critical developmental period when neurophysiological maturation and consolidation of this startle mechanism occurs. The pilot data suggests that disturbances in the acquisition and consolidation of prestimulation modulation of startle can follow exposure to extreme violence. Such a disturbance may also potentially adversely affect attention and learning, which have been implicated in children with PTSD. This experiment may begin to delineate a possible laboratory method useful in the investigation of new medications for PTSD in children and adolescents. Forty children with PTSD, 40 children without PTSD and a group of 46 normal control subjects will be tested in the laboratory at entrance to the study and at six month follow-up. Subjects will hear bursts of white noise (the startle stimulus, SS). In this prestimulation of startle experiment, the SS will be 104 dB, preceded by prestimulation at intervals known to induce startle inhibition or facilitation. Startle data from measures of the eyeblink will be correlated with clinical data collected with a battery of standardized scales. The startle response data from the groups will be evaluated using appropriate multivariate statistics.